Hydrocarbon compounds are useful for a number of purposes. In particular, hydrocarbon compounds are useful as fuels, solvents, degreasers, cleaning agents, and polymer precursors. The most important source of hydrocarbon compounds is petroleum crude oil. Refining of crude oil into separate hydrocarbon compound fractions is a well-known processing technique.
Generally speaking, a refinery receives the incoming crude oil and produces a variety of different hydrocarbon products in the following manner. The crude product is initially introduced to a crude tower, where it is separated into a variety of different components including naphtha, diesel, and atmospheric bottoms (those that boil above approximately 650° F.).
The atmospheric bottoms from the crude tower is thereafter sent for further processing to a vacuum still, where it is further separated into a heavy vacuum resid stream (e.g. boiling above 1050° F.) and a vacuum gas oil (VGO) stream (nominally boiling between 650° F. and 1050° F.). At this point the heavy vacuum resid product can be further treated to remove unwanted impurities or converted into useful hydrocarbon products.
To treat the vacuum residue stream, ebullated-bed technologies have been developed and sold, which have numerous advantages in performance and efficiency, particularly with heavy crudes. This process is generally described in U.S. Pat. No. Re 25,770 to Johanson incorporated herein by reference. The treatment of vacuum residues generally involves conversion to lighter boiling products with upgrading (contaminant reduction) of the conversion products and unconverted vacuum residue.
The ebullated-bed process comprises the passing of concurrently flowing streams of liquids or slurries of liquids and solids and gas through a vertically cylindrical vessel containing catalyst. The catalyst is placed in motion in the liquid and has a gross volume dispersed through the liquid medium greater than the volume of the mass when stationary. This technology is utilized in the upgrading of heavy liquid hydrocarbons typical vacuum residue or converting coal to synthetic oils.
The invention described herein is an improved scheme which optimally integrates heavy oil conversion/upgrading of vacuum residue and hydrotreating/hydrocracking of the conversion process vacuum gas oil. The invention may be applied to a wide range of applications including ebullated-bed reactor systems, fixed-bed systems, dispersed catalyst slurry reaction systems, and combinations thereof, including, but not limited to, petroleum atmospheric or vacuum residua, coal, lignite, hydrocarbon waste streams, or combinations thereof.
The invention comprises the creation and recycle of a selective product vacuum still product (heavy-heavy vacuum gas oil or HHVGO) back to the heavy oil conversion reactor. The recycle is a selective fraction, typically boiling in the 850-1050° F. boiling range and contains the majority of the critical contaminants including, CCR and heptane insolubles in the overall VGO product.
The remaining VGO, which is routed to a hydrotreater or hydrocracker, has significantly lower CCR and asphaltenes and is therefore easier to process. The vacuum still in this invention which separates the conversion of step products, will typically have four products including (in order of boiling range): LVGO—light vacuum gas oil; MVGO—medium vacuum gas oil; HHVGO—heavy vacuum gas oil; and vacuum bottoms—residue. The MVGO will also have less vacuum residue, which is a primary contributor to hydrotreater catalyst deactivation.
The HHVGO stream is thereafter processed, including cracking and hydrogenation when recycled back to the heavy oil conversion reactor, with the net vacuum still gas oil products consisting of LVGO, MVGO, and diesel boiling range product.